Outputs the content of the Activity WordPress page into the BP Activity directory.

bp-custom.php

<?php
/**
 * BP Custom function file.
 *
 * Add this file into /wp-content/plugins/ to customize BuddyPress.
 *
 * @see https://codex.buddypress.org/themes/bp-custom-php/
 */

// Exit if accessed directly.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Outputs the content of the Activity WordPress page into the BP Activity directory.
 */
function inclusion_du_contenu_de_la_page_wp() {
	$queried_object = get_queried_object();

	if ( $queried_object && $queried_object instanceof WP_Post ) {
		$post_content = get_the_content( null, false, $queried_object );

		remove_filter( 'the_content', 'bp_replace_the_content' );

		echo apply_filters( 'the_content', $post_content );

		add_filter( 'the_content', 'bp_replace_the_content' );
	}
}
add_action( 'bp_before_directory_activity', 'inclusion_du_contenu_de_la_page_wp' );